1. Field of the Invention
This invention relates generally to apparatus for use with communications-related equipment and more specifically to a calculation device to aid in the preparation of wire service messages which minimizes cost per word to the user.
The preferred embodiment of the present invention is intended primarily for use with circuit-switched public teleprinter networks and more specifically with the teletypewriters that are commonly used for transmitting messages over such networks. It is generally well known that there are two circuit-switched public teleprinter networks available, both of which are operated by the Western Union Company in the United States. These two networks, commonly referred to as TWX and TELEX, both provide means for utilizing teletypewriters to transmit written messages using common phone lines. TELEX and TWX teletypewriters are usually operated in conjunction with punched tape devices that use perforated paper tape to provide the opportunity to prepare and proofread messages before they are transmitted. The teletypewriter and accompanying tape perforater device are typically provided by the system operator on a rental or lease-purchase basis.
TELEX typewriters use a five channel paper tape as the input for automatic sending of messages. The tape code language is called BAUDOT and the transmission rate for TELEX machines is 66 words per minute when automatic equipment utilizes paper tape to send messages. TWX teletypewriters operate at 100 words per minute and utilize an eight channel paper tape that employs a code language commonly referred to as ASCII. The term ASCII stands for American Standard Code for Information Interchange.
In addition to the rental fees charged users for rental of the teletypewriter equipment, the service operators, such as Western Union, ITT, and RCA, charge their user customers on the basis of the amount of time required to transmit the message. In at least one instance, namely, the transmission of TWX system messages, the charge is made in full minute increments by rounding up to the next whole minute the actual time from the moment the receiving party's answer back is recorded to the moment the sender terminates the message. For example, if the total transmission time is 1.1 minutes, the time charged for sending the TWX message will be 2.0 minutes. Clearly, such rounding up to the next whole minute can result in significant additional costs to the user. By way of example, if the user were to send one international TWX or TELEX message per day, this "rounding up" procedure would add about $300.00 per year to the user's bill, assuming 260 working days, a $2.80 per minute billing rate, and a 0.45 probability factor that the message length is randomly distributed between X.1 minutes and X.9 minutes where X is any integer. This figure of $300.00 per year represents the minimum additional expense for time charges resulting from the rounding up procedure but not for time actually used for transmission of a TWX or TELEX message.
2. Prior Art
Although there are patents in the prior art which disclose devices for measuring the time required for sending a message and for measuring the length of the message to be transmitted, none of such prior art devices known to the applicant provides a suitable solution to the above-indicated problem without substantial modification and/or costly interfacing to the existing teletypewriter devices. By way of example, U.S. Pat. No. 2,150,240 to Nichols discloses a complex mechanism for the measurement of time required for the transmission of messages in a printing telegraph system. In addition, U.S. Pat. No. 2,191,798 to McCann, U.S. Pat. No. 2,481,112 to Hanley, U.S. Pat. No. 3,035,765 to Zenner et al, disclose devices relating to the broad concept of counting the time of message transmission and for displaying such time. However, no prior art devices known to the applicant discloses a portable, low-cost, microprocessor-controlled device that can accomodate both TELEX and TWX teletypewriter message systems and which can be added to such teletypewriter systems to help the operator anticipate his on-line time and avoid the aforementioned rounding up charge penalties, but without requiring significant modification to the teletypewriter.